One advantage to having a graphics card is the CPU can focus on just being a CPU and not having to help render graphics as well.
How long do you want to operate it in the field? Do you want to hot swap batteries or is shutting down and swapping batteries fine?
Toughbooks with "newer" dedicated graphics are limited to CF-31, CF-52 and CF-54.
I'm not too concerned with battery life. As I typically always have access to a plug on scenes. But knowing how awesome the battery life is on my CF53 I can only imagine it would be more than sufficient.